1. Field of the Invention
The present invention relates to a throttle control apparatus installed on an internal combustion engine, and more particularly to a throttle control apparatus for controlling the opening and closing action of a throttle valve by a driving source such as a motor and so on in response to an operation of an accelerator and for being able to perform various controls such as a constant speed driving control.
2. Description of the Prior Art
In an internal combustion engine which is provided with a carburetor, a throttle valve controls a mixed gas of air and fuel and in an internal combustion engine which is provided with an electrically controlled fuel injection apparatus, a throttle valve controls the generating power of the internal combustion engine by adjusting the intake air flow. These throttle valves are constituted so as to link with an accelerator operation mechanism including an accelerator.
In recent years, apparatuses each of which is set to open and close the throttle valve by a driving source such as a motor in response to an operation of an accelerator are proposed in contrast to the above prior art in which the accelerator operation mechanism is mechanically connected with the throttle valve. An apparatus which drives a stepping motor connected with the throttle valve in response to an operation of an accelerator is disclosed, for example, in Japanese patent application laid-open publication No. 55(1980)-145867.
On the contrary, a prior measure example against the condition under which the control of an electronic controlled actuator for driving the above stepping motor is impracticable is enumerated in Japanese patent application laid-open publication No. 59(1984)-153945. For example, a throttle shaft is set to be separated from the electronic actuator by an electromagnetic clutch for closing the throttle valve by a return spring. In this prior art, however, there is not a drive means which opens-closes the throttle valve after the malfunction of control of the electronic controlled actuator stopped and therefore there is a drawback that the vehicle can't be transfered to the suitable place for repairing. Therefore, an apparatus which overcomes the above drawback is disclosed in the Japanese patent application laid-open publication No. 59(1984)-153945.
Namely, this apparatus includes an electromagnetic clutch interposed between the throttle shaft and a rotating shaft rotated by a depression of the accelerator and arranged so as to separate both shafts from each other in its exciting condition and to connect both shafts each other in its nonexciting condition and a control circuit for detecting abnormalities of operations of the electronic controlled actuator and for stopping the supply of an electric source to the electrically controlled actuator and the electromagnetic clutch by a relay. In this apparatus, the throttle shaft is mechanically connected with the accelerator via the electromagnetic clutch when the control of the electronic controlled actuator became impracticable.
In the apparatus which is disclosed in the above Japanese patent application laid-open publication No. 59(1984)-153945, a condition which the control of the electronic controlled actuator became impracticable is detected by additional control circuit and this control circuit stops supplying the electric source to the electronic controlled actuator and the electromagnetic clutch. Then, the throttle shaft and the rotating shaft which is mechanically connected with the accelerator are connected with each other by the electromagnetic clutch after the control of the electronic controlled actuator is stopped. Now, even though the throttle valve is directly driven by the operation of the accelerator, the throttle valve maintains a condition which is connected with the actuator. In this situation, since the driving torque is not generated in the motor under the condition under which the control of the electronic controlled actuator stops, the open-close operation of the throttle valve is obtained with out hindrance in response to the operation of the accelerator.
However, the electromagnetic clutch which is used in such prior apparatus becomes large in structure and increases the cost too. Furthermore, an abnormal condition is not limited to the condition which the control of the electrically controlled actuator became impracticable and there is a possibility that the operation of the above control circuit becomes impracticable. For example, there's a possibility that the throttle valve is continued driving toward the opening position by jamming and so on. In such case, even though a switch means which is additionally provided stops supplying the electric source to the electromagnetic clutch and therefore the throttle shaft is connected with the accelerator, there is no means for driving the throttle valve toward the closing position against to tha throttle shaft which is driven by the actuator and therefore it is difficult to maintain the desired degree of the throttle valve opening.
In Japanese patent application laid-open publication No. 2(1990)-204642, a throttle control apparatus which separates a driving means from the driving source surely when the stop of the accelerator operation was detected and the excess of the then predetermined amount of the throttle valve opening was detected is proposed therein. Namely, the throttle control apparatus which can stop controlling the throttle valve by the driving source when the above conditions are detected is disclosed.
In the throttle control apparatus which is disclosed in the above Japanese patent application laid-open publication No. 2(1990)-204642, however, when the accelerator operation is released and the accelerator operation mechanism returns to the stopping position speedily, the driving means of the throttle valve is not able to follow this action. Accordingly, a condition which the throttle valve exceeds the predetermined amount of the throttle valve opening when the accelerator operation mechanism became less than the predetermined operation amount is generated. Thereby, the stop of the accelerator operation is detected and the excess of the predetermined amount of the throttle valve opening at the stopping condition is detected. As a result, the driving means is separated from the throttle valve as mentioned above and therefore the throttle control of the driving source is stopped.
In the case of a structure which the driving source is comprised of the stepping motor and which the throttle valve is driven via a reduction gear mechanism by the stepping motor, for example, it is difficult to supply a driving pulse rate enough for being able to follow the return action with the stepping motor when the accelerator operation mechanism is speedily returned to the stopping position (for example, when the accelerator is released). Thereby, in spite of the normal condition, the drive of the throttle valve of the stepping motor is stopped once. On the contrary, it is not impossible to constitute the throttle control apparatus so as to follow the above action, but it is necessary to enlarge the size of the motor and to increase the supply electric current and therefore there is no practicality.
As to such an operation, since the drive of the throttle valve resumes by the driving source when the operation of the accelerator is resumed, there is no hinderance as the throttle control. Since the useless intermittence of the electromagnetic clutch is performed, however, there's a possibility that the durability of the electromagnetic clutch and parts related to that is harmed. Furthermore, it is desirable to stop controlling the throttle valve by the driving source when a means for detecting an operation amount of the accelerator or a means for detecting an amount of the throttle valve opening broke down.